[cctalk] Rainbow 100A Video Fault (also posted on VCF)

I have been trying to diagnose a video fault on my Rainbow 100A for some time now. The monitor shows an error message and some of the attributes displayed are wrong and displayed incorrectly on every line down the screen. However, the attributes being presented to the DC012 appear to be correct and the DC012 is good (I have replaced it with a spare and with a known good one, all have the same behaviour), and yet the display is wrong. I have posted this on VCF, but would like to reach a wider audience as I am really at a loss now as to what the problem could be. Picture of the problem here: https://forum.vcfed.org/index.php?threads/video-ram-fault-on-a-rainbow-100a. 1250713/post-1418966 Description of what I have found here: https://forum.vcfed.org/index.php?threads/video-ram-fault-on-a-rainbow-100a. 1250713/post-1433618 Thanks Rob